<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>If...Else</title>
    <script>
        function myFunction() {
            var x = "";
            var time = new Date().getHours()
            if (time < 20){
                x = "Good Day"
            }else {
                x = "Good Evening"
            }
            document.getElementById("demo").innerHTML = x;
        }
    </script>
</head>
<body>
    <p>点击这个按钮，获得基于时间的问候。</p>
    <button onclick="myFunction()">点击这里</button>
    <p id="demo"></p>

</body>
</html>